This invention concerns novel pesticidal emulsions capable of being formed as stable microemulsions which may be shipped and reconstituted for application.
Pesticidal microemulsion formulations are defined as transparent thermodynamically stable dispersions of two or more immiscible liquids in each other containing varying amounts of surfactants. These formulations are classified as water-in-oil (w/o) or oil-in-water (o/w) and generally include four basic components, water, oil, surfactant and alcohol. The present invention relates to oil-in-water formulations wherein the dispersed phase, the oil phase, consists of small droplets of minces of the active ingredient surrounded by surfactant and held in a continuous aqueous phase. Pesticidal microemulsions are known in the art and U.S. Pat. Nos. 3,954,967 and 3,683,078 are illustrative of such formulations.
In general, microemulsions are produced with a large percentage of surfactant and solvent in the oil phase. The surfactant is required to cover the large surface area comprising the dispersed oil phase.
One serious problem encountered with microemulsions is the "settling out" of the emulsified material which then results in turbidity giving rise to uneven activity and general lack of acceptability. Therefore, maintenance of stability with good efficacy in the presence of an emulsifier is an important criterion for an effective and acceptable microemulsion.
It has now been found that stable pesticidal microemulsions are readily obtained by careful control of micelle size. More particularly, the formulation of this invention is a stable pesticidal microemulsion comprising
a) from about 0.01 to about 25% by weight of an insect growth regulator; PA1 b) from about 3 to about 50% by weight of one or more surfactants; PA1 c) from about 25 to about 98% by weight of water
wherein component a) is dissolved in component b) to yield an oil phase which is dispersed in component c) and said dispersed off phase forms discrete micelles in the range of about 0.001 to about 0.50 micrometers.
Illustrative of a preferred process according to the invention is a process for preparing a stable microemulsion comprising a) forming an initial oil phase comprising one or more pesticidally effective compounds and one or more surfactants; b) forming a separate aqueous phase comprising the mixture of water, chelating agents and buffers; and c) adding the aqueous phase to the oil phase until homogeneous wherein the oil phase is dispersed in the aqueous phase to form minces in the range of about 0.001 to about 0.50 micrometers.
A preferred embodiment of the present invention comprises a microemulsion formulation wherein the active ingredient includes methoprene, typically in the range from about 0.05 to about 25%. Additionally, formulations may comprise more than one active ingredients, for example methoprene and synergized pyrethrins.
It is envisaged that the microemulsion of the present invention will be used as typical for pest control but especially for control of fleas and ticks on domestic animals such as dogs and cats as a dip concentrate.
Typically and particularly with respect to dip concentrates active ingredients are formulated as emulsifiable concentrates, wherein the active ingredient is dissolved in a hydrocarbon solvent. Frequently the end user adds oil to the water phase and forms a macroemulsion. Therefore, another embodiment of the invention is a microemulsion wherein the active ingredient(s) is dissolved in one or more surfactants without a solvent and wherein water forms the continuous aqueous phase that contains the discrete micelles. Accordingly the preferred active ingredient is methoprene.
When methoprene is the active ingredient it has been found that an alkylated hydroxy benzene should be included in the oil phase to increase the stability of the methoprene. Accordingly, in a preferred embodiment the percent range on a weight basis of each component is about 0.05 to about 15 of active ingredient; 3 to about 50 of surfactant; 0.1 to about 2.0 of an alkylated hydroxy benzene; about 0.01 to about 0.5 of a chelating agent; about 0.01 to about 0.5 of a buffering agent and about 30 to about 65 water.